It is known in principle that electrical circuit breakers, which can be configured, for example, in the form of a compact circuit breaker (MCCB=molded case circuit breaker) or an open circuit breaker (ACB=air circuit breaker), can also have, in addition to a thermal magnetic trip unit (TMTU), for example, a switch apparatus and advantageously a double-break switch apparatus for interrupting a current flow of an electric current in an electrical circuit in the event of the occurrence of a tripping event, such as, for example, a short-circuit current or an overload current.
In order to interrupt the current flow of the electric current, the switch apparatus, which has, for example, a double-break multifinger contact system, is therefore rotated or pivoted about a rotation axis by way of a rotor element in such a way that the contact between the current-conducting contact rails and the multifinger contact system is interrupted. On the basis of the interruption of the current flow of the electric current, consumers or loads connected to the electrical circuit are advantageously protected from damage in the event of the occurrence of the tripping event.
Furthermore, it is known in principle that double-break contact systems and in particular double-break multifinger contact systems in a circuit breaker make it possible to connect two arcs in series and therefore enable a greater switch-off capacity. In particular, a compact circuit breaker is used, for example, for implementing a dual function, namely protecting an installation from overload and short-circuit currents and protecting lines and electrical operating devices from damage as a result of ground faults, for example. The thermal magnetic trip unit of the circuit breaker has, in a known manner, firstly a thermal tripping apparatus for protecting the electrical circuit or an electrical apparatus or an electrical device from damage owing to an overload, and secondly a magnetic tripping apparatus for protecting the electrical circuit or an electrical apparatus or an electrical device from damage owing to a short circuit.
A short circuit and in particular an electrical short circuit is generally known as an accidental or unintentionally occurring conductive connection between two or more conductive parts, and primarily between two nodes of the electrical circuit, as a result of which the electrical potential differences between these conductive parts drop to a value equal to zero or virtually zero. In particular in relation to a circuit breaker, a short circuit is an abnormal connection between two isolated phases which are intended to be isolated or insulated from one another. A short circuit results in the presence of an excessive electric current, namely an overcurrent, which can result in damage to, overheating of, a fire in or even an explosion of the electrical circuit and/or the consumer. An overload is a less extreme state in comparison with the short circuit and is rather a longer-term overcurrent state.
When using a switch apparatus comprising a double-break (multifinger) contact system, there is the problem of uniform distribution of the contact pressure among the at least two fixedly installed contacts, with which contact is made by way of the double-break contact system or the at least two switching levers. In particular owing to manufacturing tolerances or else owing to wear over the life of the switch apparatus, the position of the movable contact of the double-break switching lever can change in relation to the fixedly installed contacts. However, it is necessary for the uniform force and position distribution of the interacting contact elements to still be provided even after a large number of switching cycles and also independently of corresponding manufacturing tolerances of the individual component parts, in order to avoid different resistances at the individual contact points of the contact system. In particular when using multifinger contact systems, and in particular double-break multifinger contact systems, it is necessary for there to be such a low resistance in the case of the at least two current phases arranged parallel to one another that, advantageously, a uniform current flow distribution among the individual current phases of the multifinger contact system can be made possible, as a result of which advantageously in turn less power losses result and heating of the entire switching apparatus can be avoided.